The present invention relates to a method of estimating the angle of attack and the angle of sideslip of an aircraft.
More specifically, the invention relates to a method of estimating the angle of incidence or attack and the angle of sideslip of an aircraft.
The angle of incidence or attack and the angle of sideslip are two quantities which define parameters of the motion of an aircraft which must be monitored and controlled constantly to ensure the safety of the aircraft.
FIG. 1 shows a section through an aircraft 2 which is travelling along a direction of movement represented by a first vector 4. A second vector 6 represents the direction of an airflow which strikes the aircraft 2 longitudinally and α is the angle of incidence or attack formed by the intersection of the first vector 4 and the second vector 6.
FIG. 2 is a view of the aircraft 2 from above; the aircraft 2 is travelling along the direction of movement represented by the first vector 4. A third vector 8 represents the direction of an airflow which strikes the aircraft 2 laterally and β is the angle of sideslip formed by the intersection of said first vector 4 and third vector 8.
The angle of attack α and the angle of sideslip β should always have values below respective maximum values, for example, of 10° for the angle of attack and 5° for the angle of sideslip for a civilian transport aircraft since, if these values are exceeded, they lead to instability of the aircraft 2 which is a practically irretrievable condition.
The values of the angle of attack α and the angle of sideslip β are conventionally calculated by known techniques on the basis of measurements of air pressure outside the aircraft 2. These pressure measurements are taken by sensors arranged on the external surface of the aircraft 2. Conventional pressure sensors are commonly known as “Pitot tubes”.
Alternatively, the values of the angle of attack α and the angle of sideslip β are measured by movable “fins” which are arranged on the external surface of the aircraft 2 and are oriented in the direction in which the wind is blowing.
In sensors based on “Pitot tubes” any overheating or obstruction of the sensor is detected by control signals; in “fin”-type sensors, however, it is much more difficult to detect failure since, for example, if a “fin” is deformed or inclined there are no measurement or feedback systems that can detect the deformation or displacement.
To overcome the problems described above, more pressure sensors are put in place than are strictly necessary to take the measurements, that is, typically about 4 to 5 units, because a certain degree of redundancy is necessary so as to perform an averaging operation on the pressure measurements detected by the individual sensors and/or to compensate for any failure of a sensor. This leads to an increase in the overall costs of the aircraft 2.
Moreover, because of the large number of sensors and the fact that they are arranged projecting from the surface of the aircraft 2, they are easily visible by detection radar and are not therefore suitable for use on military aircrafts.